"The alternative to rejecting a mission with the Americans is not to do nothing - I see that [view] among many people, unfortunately also in the SPD - but rather the alternative is a European mission, if necessary without the British, if they decide for the US."

Former chancellor Gerhard Schroeder, a Social Democrat, welcomed the SPD opposition to joining the mission.

"I very much welcome the critical remarks from the SPD. A robust US-led operation could quickly escalate," Schroeder, who opposed the 2003 US-led invasion of Iraq, told the Rheinische Post newspaper.

The German government has not offered any contribution to the US-led mission but thinks it is "worth considering" a European mission and is in touch with its partners on that, a spokeswoman said on Wednesday.

"The government is reticent about the concrete US proposal and so has no made an offer," the spokeswoman told a news conference.

"For us, it is important to pursue the avenue of diplomacy... and to seek talks with Iran to achieve a de-escalation."

No Nato request

New defence minister Annegret Kramp-Karrenbauer said in a speech last week that Germany is a "reliable ally" for its Nato partners.

But she added: "We must always examine scrupulously requests for support from our partners. We mustn't affirm hastily, nor issue knee-jerk rejections."

Kramp-Karrenbauer is due to meet Nato Secretary-General Jens Stoltenberg on Wednesday.

Stoltenberg said on Wednesday that there had been no formal request for the military alliance to launch a mission in the Strait of Hormuz.